1. Field of the Invention
The present invention relates generally to electrical switchgear and, more particularly, to a pad-mounted electrical switchgear apparatus including a combination of terminators for connecting the apparatus to power lines of an electrical distribution system.
2. Discussion of the Prior Art
It is known to provide underground transmission and distribution systems which permit electrical power to be distributed to residential and commercial areas without detracting from the aesthetic appearance of the surroundings. In order to provide such underground systems, pad-mounted electrical devices such as switchgear and transformers have been developed for use in underground systems which are capable of handling relatively heavy electrical loads.
One known type of pad-mounted switchgear apparatus in present use in underground distribution systems includes an air-insulated housing enclosing a switchgear assembly, a plurality of insulated conductors extending through the housing on the source and load sides thereof, and a number of dead front cable terminators for connecting the conductors to the source side or primary power lines and the tap side or tap power lines.
As is conventional in the field of switchgear construction, the term dead front is used to define any assembly so constructed that there are no exposed live parts on the front of the assembly. In the known switchgear apparatus, each of the dead front terminators include a rubber insulated T-shaped connector and an associated "plug-in" type bushing, which together permit the terminator to be easily unplugged from the insulated conductor to permit servicing of the switchgear.
Another conventional switchgear apparatus includes the use of a switchgear assembly similar to that provided in the previously discussed apparatus, but constructed with live front terminators positioned between the insulated conductors and the primary and tap power lines. As is conventional in the field of switchgear construction, the term live front is used to define any assembly so constructed that there are exposed live parts on the front of the assembly. The live front terminators typically include exposed, energized connectors fastened to the insulated conductors and separated from the public by an enclosure to prevent inadvertent contact with the connectors.
Certain benefits and drawbacks exist with each of these known types of switchgear constructions. For example, with reference to the dead-front-terminator constructions, expensive rubber insulated T-shaped connectors are required which represent a substantial expense, especially with respect to the connectors used on the source side which must be rated to carry the relatively high currents, e.g. 600 amperes, typically carried in the primary power lines of the distribution system, e.g. a 25 kV system.
With regard to the live-front-terminator constructions, the cost of the connectors is reduced since no expensive insulators are used and no grounding or shielding provisions are made. However, in these constructions, a problem exists in that the terminators are not shielded and are energized such that a potential danger is presented to linemen working in the vicinity of the terminators. A cover is frequently provided to shield the live front terminators of these constructions, but such shields must be removed from the apparatus in order to confirm the position of the switchgear within the housing. Thus, a danger is still presented to a lineman once the cover is removed.